1. Field of the Invention
The invention relates to a downcomer for a plate column and to a plate column with downcomers of this kind.
2. Description of the Prior Art
A downcomer of this kind, a so-called xe2x80x9crotary liquid run-out apparatusxe2x80x9d, is disclosed in DE-A 2 140 899; in this downcomer the liquid running back is set into a rotary movement. In a downcomer the runback flows from one plate (xe2x80x9cvapor/liquid contact platexe2x80x9d) to the next lower one. Gas (or vapor) which is carried along must be separated from the runback in the downcomer. In the named apparatus the liquid/gas mixture flowing into the downcomer is guided by guide blades in such a manner that the separation process is accelerated thanks to the resulting rotary motion and as a result of the centrifugal force. A cup, which forms the lower closure of the downcomer and which is arranged at a distance above the next lower plate, allows the liquid flowing out of the downcomer to accumulate so that a short-circuit flow of the gas through the downcomer is prevented.
The object of the invention is to further develop the known downcomer in such a manner that the plates yield an improved effect, i.e. a greater material exchange.
The downcomer in accordance with the invention for a plate column, which is largely centrally symmetrically formed with respect to an axis pointing in the column direction, comprises: a) a downcomer opening which is located within an overflow weir on a plate and which contains the deflection elements for an inflowing liquid/gas mixture for the development of a circular flow; b) a passage part which leads downward; and c) a cup at the lower end of the passage part for accumulating the liquid flowing away. The cup contains a plurality of apertures which are designed and arranged in such a manner that a largely uniform distribution of the liquid flowing off to the next lower plate results.
In the known downcomer only a small hole is provided in the base of the cup in order that the cup can be completely emptied during an interruption in the operation. The greatest portion of the liquid flowing through the downcomer spills over the upper edge of the cup. As a result of this onward conduction of the liquid, an unfavorable xe2x80x9cshadow regionxe2x80x9d results beneath the cup: Liquid is moved away out of this region through the momentum of the onwardly conducted liquid so that, on the one hand, the liquid level is lowered there, and, on the other hand, the liquid is only slowly renewed. As a result of the lowered liquid level the xe2x80x9cshadow regionxe2x80x9d offers less resistance to the rising gas flow, so that a non-uniform gas flow arises and thus the effectivity of the plate is impaired. As a result of the slow renewal, the xe2x80x9cshadow regionxe2x80x9d makes practically no contribution to the material exchange. This defect is not present in the downcomer in accordance with the invention. The liquid flowing through the apertures in the cup base ensures an effective replacement of the liquid in the xe2x80x9cshadow regionxe2x80x9d and an increased resistance to the rising gas flow.